The present application relates generally to the field of tools for completing subterranean wells. In particular, the application relates to flapper valve retention devices.
Hydrocarbon fluids such as oil and gas are found in subterranean portions of geological formations or reservoirs. Wells are drilled into these formations for extracting the hydrocarbon fluids. Completed wells are often equipped with one or more flapper valves. The flapper valves may be safety valves or other valves used to control fluid movement. Flapper valves typically open downwards such that the pressure of the wellbore fluids bias the flapper towards a closed position.
A sleeve inside the safety valve may keep the valve open when the well is in operation. The sleeve may be maintained in position by hydraulic pressure from the surface. Should the wellhead be lost or the fluid lines from the sea bed to the platform be compromised in the case of a deep sea well, the loss of hydraulic pressure against the sleeve would result in the sleeve sliding upwardly. Accordingly, the safety valve will close to prevent further flow of wellbore fluids out of the well.
Prior to producing hydrocarbon fluids, wells must often be completed by one or more of a variety of processes. The completion processes may include, but is not limited to, perforating the well casing and/or reservoir (i.e. by use of shape charges), fracturing the formation, applying chemical treatments to the formation, or gravel packing the well, among other processes.
In many applications, a single well may pass through more than one reservoir or formation zone. In these cases, it may be desirable to complete more than one formation zone. Accordingly, a first production zone may be completed at a downhole location within a first formation. Then, a second production zone may be completed in a position above (i.e. closer to the surface) the first production zone within a second formation, or within a different area of the first formation. When carrying out the completion processes located above the first production zone, completion fluids (e.g., gravel slurries, propants, and acidifiers, among other types of completion fluids) from the second production zone may migrate downhole. Additionally, adding completion fluids in the wellbore region proximate to the second production zone may pressurize the wellbore. As a result the completion fluids from a wellbore region proximate to the second production zone may migrate to the wellbore region proximate to the first production zone. The completion fluids may ultimately migrate or flow into the surrounding first formation itself. Also, the pressurization of the wellbore may cause completion fluids remaining in the wellbore region proximate to the first production zone to migrate into the surrounding first formation.
The migration of undesired completion fluids into a production zone may damage the formation and reduce the productivity of the well. Accordingly, it may be desirable to isolate the first production zone from the second production zone during the time when the first production zone has been completed and the second production zone is undergoing completion processes. This isolation may be carried out by the use of a flapper valve or formation isolation valve for example.
In both the case of isolation and safety valves, the flapper may close in situations where it should remain open. For example, pressure deviations resulting from the completion or operation of the well may inadvertently result in the flapper partially or completely closing. Accordingly, there is a need to retain the flapper in an open position in such situations.